Piping Study

ASME B 31.1 & ASME B 31.3 CODE COMPARISON CHART PipingStudy

ASME B31.1-POWER PIPING

B31.3 uses higher allowable stress values than B31.1 (B31.1 uses an allowable of approx 117 MPa for A53-B whereas B31.3 uses about 137MPa ). B31.1 has an SIF on reducers. B31.1 includes torsional stresses in sustain case loading. B31.1 explicitly defines calculation methods for sustained and occasional loads B31.1 Code allowable stress is based upon a factor of safety of 4 the B31.1 Code has a narrow scope - Power Plants and District Heating Plants. It focuses on the steam - water loop. B31.1 on the other is about 40 years. B31.1 Power code is designed to have a higher reliability since safety of thousand people and industries will be affected. we dont compute SIF separately in B31.1,for example in B31.1 does not recognize extruded welding tee nor weldolet. If its considered then validity of using the SIF from B31.3. B31.1 uses a simplified one SIF approach (the maximum) for in and out

ASME B 31.3-PROCESS PIPING

for the same material ASME B31.3 uses relatively less allowable stresses B31.3 doesn't use SIFs on reducers B31.3 neglect torsion in sustain case laoding B31.3 calculation methods are undefined for sustained and occasional loads B31.3 Code allowable stress is based upon a factor of safety of 3 B31.3 has the greatest width of scope of any B31 Pressure Piping Code. That is why B31.3 created several "fluid services", each with specific rules. B31.3 plants generally have a plant life of of about 20 to 30 years. B31.3 Process code,with a lower factor of safety relatively, a lower reliability can be tolerated In B31.3 the SIF are computed separately for each component B31.3 uses two separate values.The B31.3 Code

plane .In the B31.1 Code, the SIF used is the LARGER of the two (inplane as applies the inplane SIF to the Inplane moment and the

compared to out-of-plane)and this larger SIF is applied to both of the bending moments occuring about mutually perpendiculat axes. B31.1 simply warns deterious effect of the corrosion when joined in cyclic loadings.

out-of-plane SIF to the out-of-plane moment (all SIF's calculated per Appendices "D" of both Codes). B31.3 instruct the user to remove the Corrosion Allowance from the Z before making sustained and occasional stress calculations.

Notes: 1) ASME B31.1 is written similer and it stays parallel with Section I of the ASME B&PV Code on most issues. 2) ASME B31.1 & ASME B31.3 ,both Codes spell out thier intended scopes and their rules are "valid" for the intended scope.ASME B31 Pressure Piping Codes are "voluntary consensus Codes". When a local building Code (which is the law -jurisdiction ) requires the use of one of the B31 Codes, Only then does it have "the force of law".Always check with your local juridiction to see what piping Code is REQUIRED by the law. 3) Code in words dont speak of factor of safety as 4 or 3 ,for exapmle:The basic allowable stress S in B31.3 is typically based on lesser of one third tensile strength and two thirds yield strength. So the 1/3 tensile at least gives a safety factor of three for S. 4) Listed are few differences .Close comparison of ASME B31.3 and ASME B31.1 you will find vast differences in materials and fabrication. 5) i = "In-plane" o = "Out-of-plane"" These terms relate to the direction of the applied moments. See Figures 319.4.4A and 4B in B31.3. The magnitude of stress in a component depends upon the direction of the applied moment. For example, an in-plane bending moment on an elbow will create a higher stress in an elbow than will an out-of-plane bending moment. B31.3 recognizes this difference by specifying different SIFs for the two moments. B31.1 takes a more simplified (and conservative) approach by specifying only one SIF (the greater of the two) for both moments (actually, the SIF applies to all three moments as B31.1 also intensifies torsional moments).